As the world's population expands and its economy grows, the rate at which atmospheric concentrations of climate changing carbon dioxide continues to rapidly increase. Fossil fuels are a causative factor in increasing pollution and in the strategic military struggles between nations. Also, fluctuating energy costs are a source of economic instability worldwide. In response, the global energy system is trying to move away from the carbon-rich fuels whose combustion produces harmful carbon dioxide. In the United States alone, it is estimated that the trend toward lower-carbon fuels combined with greater energy efficiency has reduced the amount of carbon released for each unit of economic production by nearly half.
Hydrogen is considered is a highly desirable fuel source in addressing the needs for global energy. Hydrogen is the most plentiful element in the universe (over 95%) and can therefore provide a virtually inexhaustible, clean source of energy for our planet. A fuel cell is an energy-conversion device that directly converts the energy of a supplied gas, such as hydrogen, into electrical energy. The base unit of the fuel cell is a cell having a cathode, an anode, and an appropriate electrolyte. Fuel cells have many current and potential applications such as supplying power for transportation vehicles, replacing steam turbines and power supply applications of all sorts. Despite their seeming simplicity, many problems have prevented the widespread usage of fuel cells.
Much of the initial focus in fuel cell research was directed to solid oxide fuel cell (SOFC) and proton exchange membrane (PEM) fuel cells. The SOFC has to be operated at around 1000° C. to obtain the high ionic conductivity of the solid-electrolyte which adds additional cost for thermal management of the system. The PEM fuel cell operates at 80-90° C., however, suffers from relatively low conversion efficiency and has many other disadvantages. For instance, the electrolyte for the PEM fuel cell system is acidic. Thus, noble metal catalysts are the only useful active materials for the electrodes of the system. Unfortunately, not only are the noble metals costly, they are also susceptible to poisoning by many gases, and specifically carbon monoxide (CO). Also, because of the acidic nature of the PEM fuel cell, the remainder of the materials used in the construction of the fuel cell need to be compatible with such an environment, which again adds to the cost of producing these systems. The PEM itself is quite expensive and its low conductivity at temperatures below 80° C. inherently limits the power performance and operational temperature range of the PEM fuel cell. The PEM membrane is sensitive to high temperatures, and begins to soften at 120° C. The membrane's conductivity depends on water and dries out at higher temperatures, thus causing cell failure. Therefore, there are many disadvantages to the PEM fuel cell which make it somewhat undesirable for commercial/consumer use. Both type of fuel cells require a substantial preparation time and cannot be started quickly.
The conventional alkaline fuel cell operated at room temperature has some advantages over PEM fuels cells in that alkaline fuel cells have higher operating efficiencies, use less expensive materials of construction, and have no need for expensive membranes. The alkaline fuel cell also has relatively higher ionic conductivity in the electrolyte, therefore, it has a much higher power capability. Unfortunately, conventional alkaline fuel cells still suffer from certain disadvantages. Conventional alkaline fuel cells often employ expensive noble metals catalysts in both electrodes, which, as in the PEM fuel cell, are susceptible to gaseous contaminant poisoning. The conventional alkaline fuel cell is also susceptible to the formation of carbonates from CO2 produced by oxidation of the anode carbon substrates or introduced via impurities in the fuel and air used at the electrodes. This carbonate formation clogs the electrolyte/electrode surface and reduces/eliminates the activity thereof.
While fuel cells are important to addressing global warming by eliminating carbon dioxide production, existing technologies cannot effectively store energy produced by the vast majority of alternative energy production devices. Fuel cells, like batteries, operate by utilizing electrochemical reactions. Unlike a battery, in which chemical energy is stored within the cell, fuel cells generally are supplied with reactants from outside the cell. Thus, fuel cells still require an externally supplied gas source.
The energy storage that accompanies alternative energy power generation systems (solar, wind power, etc.) is typically a battery system. Each of these alternative energies represents a discontinuous source of electrical energy in that they are effective only as long as their power source is active. For example, solar energy sources function only in daylight hours, and have peak operating performance only in direct sunlight and in the absence of cloud cover. Wind power is highly weather dependent and while many areas experience more regular winds, even these areas suffer low wind levels at least during some point of each day.
In order for each of the alternative energy generation systems to provide power on a continuous basis, energy produced during operating hours must be captured in a battery system for later use. The size of the battery system needed to guarantee continuous operation of these alternative energy systems is, however, enormous. For example, in an isolated desert environment, a minimum of 72 hours of battery storage is required. Fuel cells can supplement the battery system in this case to reduce the battery storage requirement down to 16 hours. Including existing fuel cells in an alternative energy generation system, however, significantly adds to the cost and complexity of such systems. Moreover, fuel cells alone cannot store energy or level the power output from alternative energy generation sources without the assistance from a battery or supercapacitor.
As such, there is a need for an alternative energy production system that is capable of continuous power supply and effectively couples with existing and future alternative energy production systems.